The item under the shopping cart when you only have a half pound package of sliced cheese in your cart is one of them. In a supermarket shop I had to ask if they carry fresh unpackaged rolls in the bakery section ... meanwhile I was standing right in front of them.
The ice cream shop where I had to order a small vanilla (not chocolate, mind you) cone AND a mini concrete-like ice cream item.
The snack shop where I had to take a photo of the item while I was still standing at the counter
Taking a $600+ item to a register, asking about opening up a credit card, then saying I don't want the item anymore and walking away while watching the p!$$#d off customers behind me.